Synthetic Biology | Risk assessment and risk management
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molecules (DNA, proteins, metabolites, etc.). Long term effects are to be tested by appropriate repeated-dose
studies.
90-day rodent feeding study is being widely regarded as the single most appropriate test for the detection of a
wide range of toxicological endpoints, when suitably conducted (EFSA 2008). In case of synthetic plants, the
realisation of long-term oral toxicity studies can characterise the dose-response relationship, predict chronic
toxicity effects
at human exposure levels, and test hypotheses regarding the mode of
action of synthetic plants
and derived material. Long-term toxicity studies in animals can reliably identify no-observed-adverse-effect
levels (NOAEL) used for establishing safety criteria for life-long human exposure (OECD 2009). Additional
toxicological data can provide information for studying the potential of the artificial genomic material or newly
expressed proteins derived from synthetic plants to cause carcinogenic, developmental, reproductive,
hormonal, or
neural dysfunctions in humans, and also on the toxicokinetics of the synthetic organic material.
5.3
Additional aspects in the risk assessment of plants created by synthetic
genomics
Four different subfields/techniques in the area of synthetic genomic are mentioned in scientific literature
(Schmidt 2010a):
DNA based bio-circuits (design of genetic circuits and inserting them into living cells)
Minimal genome (synthesis of genomes and transplanting them into cells)
Protocells (production of cellular containers and insertion of metabolic components)
Chemical synthetic biology (alternative chemical systems with similar biological functions)
Not all areas are equally important for the development of synthetic higher plants. Bio-circuits, minimal
genome and protocells are only relevant for single cell approaches. However, it is likely that knowledge and
expertise gained from these technologies may also be useful for the designing of synthetic plants.
For the risk assessment of DNA based bio-circuits it is not sufficient to study how the genetic element behaves
in a new environment, but to assess any interactions of the numerous genetic parts that were inserted. A
comparable counterpart for assessing a full behavioural range will not be available. Also, with minimal
genomes and protocells conventional comparators are not available, although the limited viability of minimal
genomes in the environment adds to the safety of such organisms.
Chemical synthetic biology approaches could be used for the production of synthetic higher plants. This
approach includes the chemical modification of DNA, polymerases, amino acids and proteins, but also the
identification of amino acid sequences that have a stable architecture but do not occur in nature. There are
also so-called "never-born-proteins" that could provide a lot of useful novel functions for molecular biology.
Other areas of work are the changing of translation mechanisms or the use of synthetic nucleic acids (e.g.
replacing of
base pairs, modifying sugar molecules) not occurring in nature.
The main problems in relation to synthetic plants produced by chemical synthetic biology approaches are the
high levels of uncertainties with respect to unnatural (chemically synthesised) DNA sequences, especially
synthetic nuclein base analogs. Unexplainable effects were reported with respect to a synthetic poliovirus
genome by Cello et al. (2002) mentioning that the silent mutations introduced into the virus genome had an
influence on pathogenesis by hitherto unknown mechanisms. Similar and additional unknown mechanisms are
to be expected
in synthetic plants, especially when synthetic base analogs are utilised.
In the light of recent developments in synthetic biology community a framework for risk research that
addresses four public safety issues has been proposed by the Woodrow Wilson Synthetic Biology Project: